1. Field of the Invention
The present invention relates to an image display apparatus, and, more specifically, to a projector including an image display element, a lamp for illuminating the image display element, and a fan for cooling the lamp. The invention also relates to a technique for setting a mode in which no image or a predetermined image is displayed on a display screen of the image display apparatus, without stopping the action of the lamp, and to a technique for canceling such setting.
2. Description of the Related Art
Generally, in a projector of the related art, when the user selects a mode to display no image, or a predetermined image on a display screen (hereinafter referred to as “Visual Mute Mode”), keeping a main power supply in the ON-state, a blackened image is displayed on the display screen, or an image of a desired logo, for example, is displayed on the display screen. In such case, an audio output is also stopped (hereinafter referred to as “Audio Mute”). Such muting function is especially effective in the case of a presentation and the like. The Visual Mute and the Audio Mute are collectively referred to as “A/V Mute”, hereinafter.
However, in the related art, luminance intensity of the illumination lamp is maintained even during the visual mute mode or the A/V Mute mode. Therefore, when a blackened image is displayed on the display screen of the image display element, illumination light is transmitted through the display screen and thus the image on the display screen cannot be made completely black. Further, since the cooling fan keeps operating, undesired sound of the fan stands out, and thus the effect of the visual mute or the A/V mute is not achieved sufficiently.
On the other hand, if the illumination lamp is turned OFF when setting the visual mute mode or the A/V mute mode, it takes too long to restore the display in the case of canceling the setting of the mode. This is because an extra-high pressure mercury lamp is used as a light source of the projector because of its high luminous efficacy and short arc length.
Since the extra-high pressure mercury lamp emits light by evaporating mercury encapsulated in a light-emitting tube, it takes a long time until mercury is heated up and completely vaporized, and it needs not less than 1 minute until it becomes stable. In addition, a temperature of the outer wall of the light-emitting tube is kept at about 600° C., and a vapor pressure of mercury is also high while the extra-high pressure mercury lamp is generating light, so that the temperature and the internal pressure of the light-emitting tube are not decreased immediately even when the lamp is turned OFF. Therefore, electrons can hardly move from cathode to anode even when high voltage at a high frequency is applied in such state, so that discharge cannot be started soon in the tube. As a consequence, it is impossible to relight the lamp immediately. It takes several minutes until mercury is restored to a liquid state in which the lamp is ready to relight. Therefore, switching the mode of the display screen between a display mode and the visual mute mode as desired by turning the lamp ON and OFF requires a long waiting time, and hence is inappropriate in terms of users' environments.